Comments

# Josh Williams [MS] said on June 29, 2004 7:28 PM:

Jay -- actually the /debug+ switch does have a significant effect on the code that is generated... While the /optimize[+|-] switch controls C# optimizations, the /debug[+|-] switch controls JIT optimizations (if you compile with /debug+ you'll see a funny attribute on your assembly that is commented out which indicates that the JIT should generate debuggable code. Disabling JIT optimizations is very useful for debugging purposes but will very much affect the runtime perf of an app as much of the optmization of your code is done by the JIT, not CSC (for a number of reasons, including that the JIT needs fairly non-optmized IL as input to allow it to execute quickly).

If what you really want to do is just get PDBs then the /debug:pdbonly switch is what you're looking for. Below I've included some output from a native debugger (windbg, on AMD64 - but the principal holds on all platforms) of a simple whidbey app compiled with and without the /debug+ switch (and also with /debug-). It is of note that if you're running under the VS debugger I believe that you will always see debuggable code unless you attach to the process and the code you're interested in has already been JIT'ed.


csc /out:t1.exe t1.cs
--------------------------------------------
0:000> !u 000007ff`ff1f0660
Normal JIT generated code
Test.Main()
Begin 000007ffff1f0660, size 26
sub rsp,0x28
mov rcx,0x7fff71c3030
mov rcx,[rcx]
mov rax,0x5cc00bf0
mov rax,[rax]
call rax (System.Console.WriteLine(System.String), mdToken: 06000788)
nop
add rsp,0x28
ret


csc /debug- /out:t1-debug-.exe t1.cs
-------------------------------------------
0:000> !u 000007ff`ff1d0660
Normal JIT generated code
Test.Main()
Begin 000007ffff1d0660, size 26
sub rsp,0x28
mov rcx,0x7fff71c3030
mov rcx,[rcx]
mov rax,0x5cc00bf0
mov rax,[rax]
call rax (System.Console.WriteLine(System.String), mdToken: 06000788)
nop
add rsp,0x28
ret


csc /debug+ /out:t1-debug+.exe t1.cs
--------------------------------------------
0:000> !u 000007ff`ff1d0660
Normal JIT generated code
Test.Main()
Begin 000007ffff1d0660, size 5c
sub rsp,0x38
jmp t1_debug_!Test.Main()+0xd (000007ffff1d066d)
lea ebx,[rbx]
mov rcx,0x7ffffe784e8
mov ecx,[rcx]
mov rax,0x5f095098 (JitHelp: CORINFO_HELP_DBG_IS_JUST_MY_CODE)
mov [rsp+0x20],rax
test ecx,ecx
jz t1_debug_!Test.Main()+0x30 (000007ffff1d0690)
call qword ptr [rsp+0x20]
mov rcx,0x7fff71c3030
mov rcx,[rcx]
mov rax,0x5cc00bf0
mov rax,[rax]
call rax (System.Console.WriteLine(System.String), mdToken: 06000788)
jmp t1_debug_!Test.Main()+0x55 (000007ffff1d06b5)
lea ebx,[rbx]
jmp t1_debug_!Test.Main()+0x57 (000007ffff1d06b7)
add rsp,0x38
ret

# jaybaz [MS] said on June 30, 2004 5:26 PM:

Ahh, you're right about that, Josh. I do mean that pdbonly should be the default, and that /debug- should be impossible.

I'm glad smart people read my blog, to balance me out. :-)

New Comments to this post are disabled